Corrosion induced failure of a stainless steel orthopaedic implant device

Failure investigation was carried out for the fractured orthopaedic implant device (Sherman bone plate) which fractured in the ulna of the right hand of a patient. Marked macroscopic beach marks were radiating from the pit present in the inner side of the countersunk hole. Fatigue striations, microcracks and pitting attack were noticed in the fractured site of the implant. Electrochemical potentiokinetic reactivation test on failed implant showed a significant reactivation peak indicating the presence of chromium-depleted regions. The failure of the Sherman bone plate was the consequence of corrosion fatigue due to the propagation of cracks radiating from the pit present in the crevice. The crack propagation was aggravated by the biomechanical force exerted on the implant.     

Bone remodeling around cementless hip implants

Bone remodeling results from the adaptation of bone to the stresses that act upon it. The insertion of an endoprosthesis into a femur changes the stress distribution within the femur, causing the bone to remodel. In this paper, we show how radiographic bone remodeling changes can be used to determine implant fixation and how bone remodeling changes can be quantitated by using dual-energy x-ray absorptiometry analysis as well as computer-assisted videodensitometry.     

Indications and technique of bone cutting

For cutting bones different tools and techniques are available. The question which method is most advantageous depends on the basic surgical concept, the location of the bone cut and the choice of the subsequent implant. The biological activity of the anatomical site of the cut determines how much the tissue needs to be protected, taking into consideration the vascularity of the bone and avoiding heat transfer. The surgical approach depends on the implant and should be used also for the bone cut. Specific indications are given for the oscillating saw, the Gigli saw, the osteotome, drill holes and the medullary saw.     

In vitro modeling of the bone/implant interface

BACKGROUND: The purpose of this review is to examine the usefulness of cell culture methods to model the mechanisms of bone formation on the surfaces of candidate implant materials. METHODS: The central objective is to show that in vitro methods are uniquely valuable in providing an understanding of how new bone is formed on solid surfaces. It should be emphasized, at the outset, that the use of cell culture studies as cytotoxicity assays will not be addressed, nor is it implied that cell cultures can model all the complexities of the in vivo environment. Nevertheless, by comparison with in vivo data, which are by nature retrospective, it is shown that primary differentiating osteogenic cell cultures, derived from bone marrow, illustrate a sequence of extracellular matrix elaboration events that characterize the establishment of the interface between newly formed bone and solid surfaces. These solid surfaces either may be implant materials, or indeed previously formed bone matrix, which has been resorbed during normal bone remodeling events. In each case the first biologically derived matrix at these sites is a morphologically distinct collagen fibre-free extracellular matrix, which, in bone histology has been referred to for > 100 years as a cement line. RESULTS: The sequence starts with secretion and adsorption to the substratum of organic components, of which the major proteins are osteopontin and bone sialoprotein. Mineralization of this matrix occurs by the seeding of nanocrystalline calcium phosphate, which precedes the appearance of morphologically identifiable collagen fibres. This is clearly contrary to the dogma that collagen is necessary for mineralization of bone, but is in agreement with specific cases of other, particularly dental, calcified connective tissues. Although collagen is synthesized by the differentiating osteogenic cells that elaborate the cement line interface, it is not adsorbed to the underlying solid surface. Following the elaboration of the cement line matrix, collagen fibre assembly occurs and is then mineralized to produce morphologically identifiable bone matrix. CONCLUSION: Key elements of this sequence of events can be seen at the interface of implants retrieved from in vivo experiments, which indicates that these in vitro methods not only mimic known in vivo phenomena, but also provide a mechanistic understanding of bone elaboration at implant surfaces. However, distinction is drawn between the events of new bone formation at implant surfaces and other bone/implant morphologies, which are unrelated to de novo bone formation at the implant surface. Finally, this new information emerging from bone marrow cell culture studies demands a re-examination of the concepts of bone-bonding and nonbonding implant materials.     

Clinical and histologic evaluation of an active "implant periapical lesion": a case report

A new entity called "implant periapical lesion" has recently been described. This lesion could be the result of, for example, bone overheating, implant overloading, presence of a preexisting infection or residual root fragments and foreign bodies in the bone, contamination of the implant, or implant placement in an infected maxillary sinus. This case report describes a titanium implant that was placed in the maxillary premolar region. A fenestration involving the middle portion of the implant was present. After 7 months, the apical portion of the implant showed radiolucency. This lesion rapidly increased in size and a vestibular fistula appeared. A systemic course of antibiotics was not successful, and the implant was then removed. The histologic examination showed the presence of necrotic bone inside the antirotational hole of the implant. The etiology of the implant failure in this instance could possibly be related to bone overheating associated with an excessive tightening of the implant and compression of the bone chips inside the apical hole, producing subsequent necrosis.     

Biodegradable interlocking nails for fracture fixation

Serious problems such as stress shielding, allergic reactions, and corrosion are associated with the use of metallic fracture fixation devices in fractured long bones. Metal implants often are removed during a second retrieval operation after fracture healing has completed. A biocompatible implant that degrades slowly during implantation would obviate the need for a second operation and save the patient from considerable physical, psychologic, and financial discomfort. The biodegradable implant must provide the fractured limb sufficient support for a certain time, allowing early loading. A gradual transfer of load from the biodegradable implant to the bone would result in a better product of bone healing and avoid stress shielding. In an animal model using adult sheep, two types of biodegradable polymer interlocking nails were tested in comparison with a stainless steel interlocking nail. Fracture healing, mechanical properties of the bones, degradation behavior in vivo and in vitro, and tissue response were monitored during a 2 1/2-year followup study. To detect shifts in acid base relations caused by the release of acid compounds, pH measurements were performed. Fracture healing was unimpaired, and the mechanical test results of all three groups were excellent. Histologic analysis showed a mild inflammatory response, but no pH shifts were observed. The results of this study justify additional research on these promising materials.     

Available bone is the foremost criterion in the insertion of endosteal implants

The foremost criterion in the insertion of endosteal implants is bone availability. Implant dentists should consider first the amount of available bone of the edentulous ridge where the endosteal implant will be inserted. A common error and cause of many implant failures is the dentist's use of an implant modality which is not indicated for the density and morphology of the available bone in the edentulous ridge. Implant modality/system is not the primary criterion in the insertion of endosteal implants. Before the dentist inserts an endosteal implant, he should gauge or measure the amount of bone where the implant is intended to be placed. It should be measured in width, height, length, trajectory, and implant-crown ratio. After recording the measurements of the available bone, these should be placed in different categories to serve as guides in implant selection. If there is not enough bone for the endosteal implant, bone modification should be performed. This can be done either by osteoplasty or ridge augmentation with the use of bone grafting materials. Aside from the amount of available bone in the edentulous ridge, another very, very important thing that should be considered is the quality or its density. Any biocompatible implant demonstrates some osseointegrated surfaces depending upon the bone type into which it is placed and the loads placed upon it. Implant body must exhibit a macrogeometry suitable for acceptable levels of force transfer to the surrounding tissues as well as for implantation into a bony site of a particular anatomic size.     

Biologic attachment of an allograft bone and tendon transplant to a titanium prosthesis

An Achilles tendon allograft with its bony insertion was used to bridge a Titanium implant, containing an endoprosthetic tendon anchor, and the sheep biceps muscle. Twelve sheep were operated on unilaterally and followed up clinically and histologically for 2, 4 (n = 2), 8, and 12 months (n = 4). Full function of the front limb was regained after 8 to 12 weeks. There were no signs of mechanical loosening at all times. The morphologic changes at the bone block and implant fixation site were an initial revascularization of the allograft bone, which was observed at 2 months and enhanced at 4 months but occurred without any evidence of bone remodeling. This was changed in all specimens taken at 8 and 12 months where intensive new bone development, remodeling, and bone ingrowth in the titanium implant was found. Bone mass was shifted significantly to the tendon insertion half of the bone block because of a creeping substitution of the cancellous allograft bone and bone ingrowth to the implant. Overall bone mass slightly decreased with time but resorption of allograft bone outweighed new bone development only at lesser loaded areas. Transplantation of a bone and tendon allograft to an implant resulted in a revitalized, mechanically stable, and biologically anchored compound.     

Biomechanical and histologic alteration of facial recipient bone after reconstruction with autogenous bone grafts and alloplastic implants: a 1-year study

Potential alteration of the underlying recipient bone resulting from a graft or implant has significant clinical relevance. The present study was designed to evaluate the biomechanical and histologic alteration of facial recipient bone with autogenous bone graft and alloplastic implants over a 1-year period. The bilateral arches of 15 rabbits were randomized between four groups: (1) control (n = 6), subperiosteal exposure of the zygomatic arch was made; (2) onlay (n = 12), bone graft was placed as an onlay to the zygomatic arch; (3) inlay (n = 6), bone graft was placed as an inlay within the zygomatic arch; (4) implant (n = 6), a stainless steel plate was placed as an onlay to the zygomatic arch. Animals were killed 1 year after grafting. In the onlay groups, all steel implants and half of the onlay bone grafts (n = 6) were separated from the zygomatic arch; the remaining onlay bone grafts (n = 6) were left on the zygomatic arch. Three-point breaking strength was measured through the center of the graft/implant site on the zygomatic arch, followed by histologic evaluation and histometric assessment of residual bone density. The findings demonstrated no difference in the breaking strength per unit bone area between the control zygomatic arch group and the onlay group in which the bone graft was left in place. Breaking strength of the zygomatic arch in the former two groups was significantly greater than that in either group in which the onlay bone graft or implant had been removed, and was also greater than the breaking strength in that group in which inlay bone had been placed (p < 0.05). Histologic assessment showed full-thickness conversion in architecture of the zygomatic arch from compact to woven bone beneath onlays of either autogenous bone graft or steel implant; histometric assessment demonstrated an accompanying decrease in bone density in the latter groups relative to the control zygoma (p < 0.05). We conclude that onlay autogenous bone graft and alloplastic implants to the facial skeleton induce transformation of both graft and recipient bone from compact to woven architecture, accompanied by a reduction in bone density. The biomechanical strength of recipient facial bone is significantly weakened if an onlay bone graft or implant is removed. Weakening occurs per unit area of remaining bone, and is therefore independent of any thinning that may occur within the recipient bone because of graft/implant placement. These findings may impact upon decisions to augment stress-bearing regions of the facial skeleton with bone graft or implants, particularly if the graft/implant may eventually require removal.     

Influence of bone quality on stress distribution for endosseous implants

The present study examined the influence of bone quality on the transmission of occlusal forces for endosseous dental implants. Employing the finite element method, the study modeled a 3.75 x 10-mm threaded implant placed in a 12 x 11 x 8-mm section of bone. By varying the elastic parameters assigned to the bone elements, four bone quality categories were established. A load of 100 N was applied at the occlusal surface of the restoration at a 30 degrees angle to the vertical axis of the implant. Maximum von Mises stress concentrations (sigma Emax) were observed to be located in the marginal bone at the coronal aspect of the implant fixture in all four cases. Values of sigma Emax were 13.7 MPa for type 1 bone, 15.8 MPa for type 2 bone, 20.1 MPa for type 3 bone, and 26.5 MPa for type 4 bone. Magnitude of the stresses in bone was strongly correlated (r = 0.997) with computed displacement of the implant system. This analysis predicts that placement of implants in bone with greater thickness of the cortical shell and greater density of the core will result in less micromovement and reduced stress concentration, thereby increasing the likelihood of fixture stabilization and tissue integration.     

Immediate implant surgery: three-year retrospective evaluation of 50 consecutive cases

Since August 1989, 35 consecutive patients were treated with immediate implants to replace 50 teeth requiring extractions as a result of root fractures, endodontic instability, nonrestorable carious lesions, or periodontal disease. Defects relative to the implant were morphologically grouped and were treated for bone regeneration with demineralized freeze-dried crushed cancellous bone (DFDBA), e-PTFE membrane, or both. Thread exposure initially ranged from 4 to 20 threads, while implant lengths varied from 8.5 to 18 mm. The mean implant length was 15 mm, with mean thread exposure of 11.34 threads, or 54% of the threaded length of the implant. Reentry confirmed 100% thread coverage in all but one implant in the no-wall group treated with DFDBA alone. Histologic evaluation of three cases confirmed viability of the regenerated bone. The patients were followed through April 1993, with 49 implants (98%) remaining osseointegrated and functional, supporting the predictability of immediate implant placement. The age of the patients ranged from 16 to 80 years, hence implant placement considerations relative to adolescents are also discussed.     

Repair of bone defect in primate mandible using a bone morphogenetic protein (BMP)-hydroxyapatite-collagen composite

The purpose of this study was to evaluate a hydroxyapatite (HA)-collagen (Col)-bone morphogenetic protein (BMP) composite as an osteoinductive bone substitute. Partially-purified BMP from bovine bone was mechanically mixed with highly purified type I collagen from calf dermis and then subsequently mixed with pure synthetic hydroxyapatite granules or block. The HA-Col-BMP composite, or the HA-Col composite as a control, was implanted in a surgically-induced mandible bone defect (6 x 7 x 10 mm) in an adult Japanese monkey. The mandible was excised three months after implantation and studied histologically. The BMP-containing implant induced much more new bone than the control implant in all experimental animals of each group, with either HA granules or HA block. Newly formed bone was attached tightly to HA and infiltrated deeply into the pores of the HA of the BMP-containing implant, while fibrous tissue existed between the host bone and HA in the control implant. Thus, we conclude that an HA-Col-BMP composite could be a superior biomaterial for a bone substitute.     

Acute liver failure

PURPOSE: This article reviews the literature on radiographic imaging techniques and image interpretation for dental implant treatment. MATERIALS AND METHODS: MEDLINE was used to identify published peer-reviewed literature for this report. RESULTS: Radiographic images are indispensable in the evaluation of osseous structures when planning treatment for dental implants. Potential bone sites for implant placement can be assessed clinically by means of palpation or probing through the mucosa; however, diagnostic imaging provides the best means for indirectly measuring bone dimensions. After healing of the implant site, the application of radiology is useful to verify the amount of bone adjacent to the implant and that the transmucosal abutments fit the implant. Upon completion of the implant prosthesis, radiology may be used to monitor initial and long-term success of implant treatment. CONCLUSION: Recommendations for the application of radiology over the course of treatment are made for various implant cases ranging from the overdenture to the single-tooth implant.     

Inhibition of eFGF expression in Xenopus embryos by antisense mRNA

This pilot study analyzed the bone reactions to early loaded titanium plasma-sprayed implants. A total of 24 titanium plasma-sprayed implants (12 in the maxilla and 12 in the mandible) (Primary Healing Implant, Legnano) were inserted into four Macaca fascicularis monkeys with instruments specially designed to obtain a precise fit of the implant in the bone socket. A metal superstructure was cemented into 10 mandibular and 10 maxillary implants 15 days after implant insertion. The four remaining implants were used as controls. Eight months after implant placement, a block section was carried out, the defect was filled with nonresorbable hydroxyapatite, and all 24 implants were retrieved. The implants were treated to obtain thin ground sections that were examined under normal and polarized light. Histologic analysis showed that bone was observed around the implant surface in all implants. Morphometric analysis demonstrated that bone lined 67.2% (SD = 3.1%) of the maxillary implant surface, and 80.71% (SD = 4.6%) of the mandibular implant surface. No differences were found in the percentage of bone-implant contact in the control implants. In the loaded implants, however, the bone around the implants had a more compact appearance. The study demonstrated that it is possible to obtain a high percentage of bone-implant contact in early loaded titanium plasma-sprayed implants.     

GBR with an e-PTFE membrane associated with DFDBA: histologic and histochemical analysis in a human implant retrieved after 4 years of loading

As a result of a fracture to the cemented post and core, a pure titanium implant was extracted from a 54-year-old patient after 4 years of clinical loading. At implantation, the implant was positioned into an extraction socket and the defect was treated with an e-PTFE membrane associated with a DFDBA graft. At retrieval the implant underwent histologic and histochemical examination to assess the characteristics of the regenerated bone after 4 years of prosthetic loading. The implant showed an angular bony defect at the smooth collar, but the bone-implant direct contact rate seemed to be elevated in the remaining implant surface. Normal transmitted and polarized light examinations demonstrated that most of the DFDBA particles were resorbed and substituted by vital newly formed bone. The regenerated bone appeared compact with secondary osteons and large haversian canals; however, some partially mineralized remnants residuated in the spaces, between the osteons. Within the limits of this study, the authors concluded that DFDBA can be substituted by the host bone, but the rate of substitution is very slow and not complete after 4 years. From a clinical point of view, however, the load-bearing capacity of the bone regenerated with the membrane technique associated with DFDBA appeared to be similar to that of normal bone.     

Principles of stable internal fixation

The results of internal fixation can be adversely affected by implant failure before union takes place. The survival of an internal fixation device depends upon load transfer from fragment to fragment. Techniques that do not provide such a load sharing between implant and bone will lead to failure of the implant. For example, absence of contact between cortices opposite the plate will increase the forces acting on the device which will either pull out, shear or break. This review focuses on the methods of applying implant to bone to achieve stable fixation and thus restore early function without sacrificing reduction and union.     

Use of X-ray diffraction for studying the temperature dependence of the Young modulus of protein crystals

Conventionally, for dental reconstruction after bone grafting of the congenital residual alveolar cleft, a fixed prosthesis or removable partial denture is used. In this paper, residual alveolar cleft reconstruction with an osseointegrated implant following secondary bone grafting is described. The patient underwent secondary bone grafting of the residual alveolar cleft at the age of 18 years. One osseointegrated implant was placed in the bone bridge 8 months after bone grafting. No problems up to 1 year after the fabrication and placement of the fixed prosthesis have been observed.     

Homogenized stress analysis in a dental implant system

In this study, the stress state occurring at each trabecular due to three different types of dental implant is investigated by a homogenization technique, in which the trabecular structure is assumed to be composed of repeating hexagonal units. This technique helps make a proper material model of bone and to analyse such a non-homogeneous structure at the level of an individual microstructural unit. Stress analyses with the homogenization technique show a much higher stress level in the sponge bone, compared to those with conventional FEM. It also shows that even a minor lateral force results in crucial stresses in the dental implant system. The stress states of the mandible with a hemisphere-rooted implant and a wedge type implant show similar levels, while those with a rectangular-rooted implant result in higher stresses. It is suggested that the distance between the implant tip and cortical bone be kept far enough apart to prevent stress concentrations in the mandible.     

不同弹性模量的基台-种植体组合对周围成骨性能的影响

利用有限元分析软件计算了不同静力作用下的多种基台-种植体周围骨组织的应力分布.模拟结果显示, 基台-种植体组合中Ti6Al4V钛合金-聚醚醚酮(TC4-PEEK)相对于其他实验组其应力集中程度现象可以有效降低, 周围骨组织的应力分布较为均匀, 最大应力值为40~60 MPa.在轴向加载条件下, 不同基台-种植体系统中PEEK种植体的应力水平较小, 而周围骨组织应力水平较大; 在斜向45°加载条件下, 相对于其他两种基台-种植体系统, TC4-PEEK的应力水平更低, 其周围骨组织中的皮质骨承受的最大应力值为55 MPa, 松质骨承受的最大应力值为5 MPa, 综合来看的应力水平最小, 有助于骨沉积和成骨量增加, 从而有效提高种植体的界面稳定性.      

Biocompatibility of nitinol alloy as an implant material

The biocompatibility of nitinol alloy as a potential implant material was investigated through in vivo studies on beagles. A high-purity alloy was fabricated into prototype bone plates and implanted into the femurs of beagles. Commercial cobalt-chromium (Co-Cr) alloy bone plates served as reference controls, an additional control data were obtained from beagles subjected to "sham" operations. The bone plates were removed from the animals and examined after exposures of 3, 6, 12, and 17 months. There was no evidence of either localized or of general corrosion on the surfaces of the bone plates and screws. Gross clinical, radiological, and morphological observations of the tissue at the implantation sites during the autopsies uncovered no signs of adverse tissue reactions resulting from the implants. Histological analyses were performed on samples of muscle and bone adjacent to the implantation sites, and of tissues removed from such organs as the liver, spleen, brain, and kidneys. No significant differences were noted between samples taken from controls and those taken from dogs exposed to the implants. Neutron activation analyses were carried out on suitable samples. The analysis data suggest that there is no metallic contamination in the organs due to the implants; however, there does appear to be some chromium contamination from the Co-Cr alloy implants in the adjacent bone. On the basis of the totality of the data, it is concluded that nitinol alloy is sufficiently compatible with dog tissue to warrant further investigation of its potential as a biomaterial.